Recently, it is noted to use ferroelectric film as the dielectric film of capacitors. An FeRAM (Ferroelectric Random Access Memory) including such ferroelectric capacitors is a nonvolatile memory having characteristics, such as being operative at high speed and having low electric power consumption, good write and read endurance, etc. and is prospective.
However, the ferroelectric capacitor has the characteristic that the characteristics are easily deteriorated by hydrogen gas and water from the outside. Specifically, it is generally known that the ferroelectric capacitor of the standard FeRAM, having the lower electrode of Pt film, the ferroelectric film of PZT film and the upper electrode of Pt film substantially loses the ferroelectricity of the PbZr1-XTiXO3 film (PZT film) when the substrate is heated to around 200° C. in an atmosphere of an about 40 Pa (0.3 Torr) hydrogen partial pressure. It is known that the ferroelectricity of the ferroelectric film of the ferroelectric capacitor is much deteriorated when thermal processing is performed with the ferroelectric capacitor adsorbing water or with water being present near the ferroelectric capacitor.
Because of these properties of the ferroelectric capacitor, in the process for fabricating the FeRAM, processes which generate small amounts of water and are made at low temperatures as far as possible are selected as the processes following the formation of the dielectric film. As the process for forming the inter-layer insulation film, the film forming processes, such as CVD (Chemical Vapor Deposition), etc., using raw material gases which generate relatively small mounts of hydrogen are selected.
Furthermore, as the technique for preventing the deterioration of the ferroelectric film due to hydrogen and water are proposed the technique of forming aluminum oxide film covering the ferroelectric capacitors, the technique of forming aluminum oxide film on an inter-layer insulation film formed above the ferroelectric capacitors. Aluminum oxide film has the function of preventing the diffusion of hydrogen and water. These proposed techniques can prohibit hydrogen and water from arriving at the ferroelectric film, and the deterioration of the ferroelectric film due to hydrogen and water can be prevented. These techniques are disclosed in, e.g., Patent References 1 to 7.
[Patent Reference 1]
Japanese Patent Application Unexamined Publication No. 2003-197878
[Patent Reference 2]
Japanese Patent Application Unexamined Publication No. 2001-68639
[Patent Reference 3]
Japanese Patent Application Unexamined Publication No. 2003-174145
[Patent Reference 4]
Japanese Patent Application Unexamined Publication No. 2002-176149
[Patent Reference 5]
Japanese Patent Application Unexamined Publication No. 2003-100994
[Patent Reference 6]
Japanese Patent Application Unexamined Publication No. 2001-36026
[Patent Reference 7]
Japanese Patent Application Unexamined Publication No. 2001-15703